MIC38C42 Micrel Semiconductor, MIC38C42 Datasheet - Page 8

• Manufacturer Part Number: MIC38C42
• Description: BiCMOS Current-Mode PWM Controllers
• Manufacturer: Micrel Semiconductor

MIC38C42/3/4/5
ripple. This inductance value also improves circuit efficiency
by reducing the flux swing in L1.
Magnetic components are carefully chosen for minimal loss
Synchronous Buck Converter
Refer to figure 2. This MIC38C43 synchronous buck con-
verter uses an MIC5022 half-bridge driver to alternately drive
the PWM switch MOSFET (driven by GATEH, or high-side
output) and a MOSFET which functions as a synchronous
rectifier (driven by the GATEL, or low-side output).
The low-side MOSFET turns on when the high-side MOSFET
is off, allowing current to return from ground. Current flows
through the low-side MOSFET in the source to drain direc-
tion.
MIC38C42/3/4/5
Test
Line Regulation
Load Regulation V
Efficiency
Output Ripple
2200
6.8k
pF
Conditions
V
V
V
47k
3.3k
10k
IN
IN
IN
IN
= 26V to 80V, I
= 48V, I
= 48V, I
= 48V, I
10k
300k
4.3k
4.7nF
0.15µF
O
O
O
= 0.2A to 2A
= 2A
= 2A (20MHz BW)
COMP
FB
ISNS
RT/CT
MIC38C43
O
*Locate near the MIC38C43 supply pins.
Figure 2. 100kHz, Synchronous Buck Converter
= 2A
VOUT
VREF
GND
VDD
0.1µF*
MKS2
0.1µF
470µF
Results
100mV
25V
0.5%
0.6%
90%
+12V
8
NC
NC
NC
at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type
material toroids. L1 is wound on a Siemens N49 EFD core.
1. Custom Coils, Alcester, SD tel: [phone]
2. Energy Transformation Systems, Inc. tel: [phone].
The on-state voltage drop of the low-side MOSFET is lower
than the forward voltage drop of an equivalent Schottky
rectifier. This lower voltage drop results in higher efficiency.
A sense resistor (5mΩ) is connected to the driver’s high-side
current sense inputs to provide overcurrent protection. Refer
to the MIC5020, MIC5021, and MIC5022 data sheets for
more information.
Symbol
CT1
T1
L1
VDD
FLT
EN
IN
CT
GND
MIC5022
GATEH
GATEL
SH+
SH–
SL+
SL–
VB
Custom Coil
4923
4924
4925
0.1µF
SMP60N06-14
1
5mΩ
35µH
ETS
ETS 92420
ETS 92419
ETS 92421
2
1000µF
Low ESR
5V, 8A
V
August 2000
OUT
Micrel